The subject matter disclosed herein relates generally to radiation detectors for medical imaging, such as in Low-Flux applications in Nuclear Medicine (NM), whether by Single Photon Emission Computed Tomography (SPECT) or by Positron Emission Tomography (PET), or as radiation detectors in High-Flux applications as in X-ray Computed Tomography (CT) for medical applications and for non-medical imaging application such as in baggage scanning.
Room temperature pixelated radiation detectors made of semiconductors, such as Cadmium Zinc Telluride (CdZnTe or CZT), are gaining popularity for use in medical and non-medical imaging. These applications dictate that these detectors have to exhibit both high energy resolution and high sensitivity. Since these detectors form a crucial part of complex imaging systems they should be highly reliable with a cost low enough to suit market requirements.
Semiconductor radiation detectors generally include two surfaces, one having a plurality of pixelated anode electrical contacts, and the second having a monolithic cathode electrical contact. Prior to the application of the electrical contacts, the first and the second surfaces are commonly etched by chemical wet etching. For CZT radiation detectors, the wet etching is performed in order to remove the mechanical damage from the first and second surfaces. This damage is introduced by previous fabrication steps where the semiconductor wafers have been sliced and polished to form surfaces. Furthermore, the wet etching forms tellurium rich surfaces, which is used to produce electrical contacts with favorable characteristics.
The tellurium rich first surface on which the anode contacts are applied have non-metallized regions between the anode contacts. The excess tellurium in these regions causes reduced surface resistance between the contact pads. It has been shown in an article by Bolotnikov et al., “Charge Loss Between Contacts Of CdZnTe Pixel Detectors”, Nucl. Instr. and Meth. A, (1999), 432, 326-331 that these low surface resistance surfaces between the anode contact pads cause charge loss of the events attracted to the anode contacts. This incomplete charge collection causes impairment of the energy resolution and the sensitivity of these detectors. Furthermore, low surface resistance has been shown to degrade the signal stability over time. This instability results in detectors that are unreliable.